GNU ar warning about deterministic mode

GNU ar currently produces the following string of warnings:
Warning: Archive 'libefi.a' seems to have been created in
deterministic mode.
'<file>.o' will always be updated. Please consider passing
the U flag to ar to avoid the problem. This patch fixes the issue.

Signed-off-by: Pete Batard <pete@akeo.ie>
Signed-off-by: Nigel Croxon <noxorc@users.sf.net>

Make.defaults

@@ -156,6 +156,7 @@ CFLAGS  += $(ARCH3264) -g -O2 -Wall -Wextra -Werror \
            -fno-stack-check
 endif
 
+ARFLAGS += -U
 ASFLAGS += $(ARCH3264)
 LDFLAGS	+= -nostdlib --warn-common --no-undefined --fatal-warnings \
 	   --build-id=sha1